Water Vapour Promotes CO2 Transport in Poly(ionic liquid)/Ionic Liquid-Based Thin-Film Composite Membranes Containing Zinc Salt for Flue Gas Treatment

Marek Tanczyk,Paul Inge Dahl,Daria Nikolaeva,Alessio Fuoco,Jolanta Jaschik,Marius Sandru,Johannes Carolus Jansen,Sandrine Loïs,Ivo F.J. Vankelecom

doi:10.3390/app10113859

Abstract

A poly(ionic-liquid) (PIL) matrix can be altered by incorporating additives that will disrupt the polymer chain packing, such as an ionic liquid (IL) and inorganic salts to boost their exploitation as materials for membrane production to be used in CO2 capture. Herein, potential of PIL/IL/salt blends is investigated on the example of poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf2N]) with N-butyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ([Pyrr14][Tf2N]) and zinc di-bis(trifluoromethylsulfonyl)imide (Zn[Tf2N]2). Composite material with IL and a higher amount of Zn2+ showed an increase in the equilibrium CO2 sorption capacity to 2.77 cm3 (STP)cm −3 bar−1. Prepared blends were successfully processed into thick, dense membranes and thin-film composite membranes. Their CO2 separation efficiency was determined using ideal and mixed-gas feed (vol% CO2 = 50 , dry and with 90% relative humidity). The dominant role of solubility in the transport mechanism is confirmed by combining direct gravimetric sorption measurements and indirect estimations from time-lag experiments. The maximum incorporated amount of Zn2+ salts increased equilibrium solubility selectivity by at least 50% in comparison to the parent PIL. All materials showed increased CO2 permeance values by at least 30% in dry conditions, and 60% in humidified conditions when compared to the parent PIL; the performance of pure PIL remained unchanged upon addition of water vapor to the feed stream. Mixed-gas selectivities for all materials rose by 10% in humidified conditions when compared to dry feed experiments. Our results confirm that the addition of IL improves the performance of PIL-based composites due to lower stiffness of the membrane matrix. The addition of Zn2+-based salt had a marginal effect on CO2 separation efficiency, suggesting that the cation participates in the facilitated transport of CO2.

Highlights

Poly(ionic liquid)-based membranes for CO2 capture overcome the possible problems of ionic liquid (IL) leaching from the supported IL membranes [1]
Effective CO2 selective materials prepared from commercially available P[DADMA][Cl] were successfully converted in poly(ionic liquid)-based composite materials with improved CO2 sorption properties
The time-lag experiments show that the addition of the IL improves the CO2 diffusivity in the Poly(ionic liquid)s (PILs)/IL composite

Summary

Introduction

Poly(ionic liquid)-based membranes for CO2 capture overcome the possible problems of ionic liquid (IL) leaching from the supported IL membranes [1]. Poly(ionic-liquids) (PILs) demonstrate a considerable reduction of CO2 sorption capacity and diffusion rates due to higher stiffness of the polymer matrix, leading to lower CO2 transport [2,3]. Poly(ionic liquid)s (PILs) have recently prompted extensive practical aspirations due to their potential to combine the large CO2 sorption capacity of ionic liquids (IL) and good processability of conventional polymers [6,7,8]. The IL monomers should have a high degree of purity, and undergo elaborate synthetic procedures to produce large amounts of PILs with sufficient molecular chain length, which might present a critical factor in their further employment as selective membranes for CO2 capture [13]

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Results

Conclusion